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Friday, July 1, 2011

Summer of the pill: Will the pill mess up my ability to detect my One True Love?

Should I advise recently single ScarJo to stay
off the pill to find her next beau? From here.

Imagine you are a single, heterosexual woman. You meet a nice man at the driving range, or on a blind date. You like him and he likes you. You date, you get engaged, you get married. You decide to have a child together, so you go off the pill. One morning you wake up and look at your husband, and it’s like seeing him through new eyes. Who is this stranger you married, and what did you ever see in him?

After some articles made the news when they suggested mate preferences change on hormonal contraception, this seemed to be the scenario in the heads of many women. Is my pill deceiving me? What if my birth control is making me date the wrong man?

Several articles over the years have demonstrated that women prefer men with more masculine features at midcycle, or ovulation, and more feminine features in less fertile periods. Based on body odor, women and men also often prefer individuals with MHC (major histocompatibility complex) that are different from theirs, which may be a way for them to select mates that will give their offspring an immunological advantage. These findings have been replicated a few times, looking at a few different gendered traits. And as I suggested above, other work has suggested that the birth control pill, which in some ways mimics pregnancy, may mask our natural tendency to make these distinctions and preferences, regarding both masculinity and MHC (Little et al. 2002; Roberts et al. 2008; Wedekind et al. 1995).

On the one hand, I think it’s both interesting and important to consider the implications of the birth control pill beyond just contraception. Hormones are messages, so any cells that have receptors for these messages, like specialized mailboxes, can receive them. The pill is made of synthetic versions of estradiol and progesterone, and there are estradiol and progesterone receptors in your brain. And yes, these hormones do change your brain, both during the natural cycle and on hormonal contraception; Scicurious has written well on this in the past.

Jolie, had she been on the pill and chosen her mate
differently. From here. Yes, looks to be a real pic.

On the other hand, I have a lot of questions: First and most important to me, how does any of this translate to non-straight women? I find the constant focus on mate choice between men and women a bit exhausting, and am not sure we can assume non-straight relationships to work the same way. Next, how well do preferences over the cycle map on to actual choices for mates, short term or long term? If we happen to find Brad Pitt more attractive than Justin Bieber at midcycle, does that mean no one will do but Brad Pitt? And finally, what are all the factors that we need to consider in mate choice besides a deep voice or square jawline (again, especially if you try to expand your thinking beyond straight relationships)?

I’ll start with the last two questions that deal with mate preference versus ultimate mate selection. As you all might expect, women and men choose mates for lots of reasons, not just masculinity or complementary immune systems. Bereczkei et al (1997) looked at singles ads and found women often sought mates with high parental care. In a separate singles ad evaluation, Pawlowski and Dunbar (1999) found that women mostly selected men of high resource potential who were interested in long-term relationships (either unlikely to divorce or unlikely to die within twenty years), where men selected women by markers of fecundity (ability to have babies). In a sample of 18-24 year old straight people in the US, Buston and Emlen (2003) found that most people selected mates who had similar characteristics to themselves. And a speed dating sample showed that people under those conditions selected dates based on easily observable traits, like physical attractiveness (Kurzban and Weeden 2005).

Now on to the fact that all of this research is on straight people. I found very little on lesbian women and the menstrual cycle... but what I found was very cool! Brinsmead-Stockham et al (2008) found that, like heterosexual women, lesbian women are quicker to identify unknown faces at midcycle, as long as they were the faces of the sex they preferred. So straight women were good at identifying male faces, lesbian women good at identifying female faces. Burleson et al (2002) found that sexual behavior in lesbian and straight women was mostly similar through the menstrual cycle, with both peaking at midcycle.

So, mate preference may be about telling a research assistant who is the hottest to you at a particular point in your cycle. And it is a fairly robust and consistent finding. However, when it comes to ultimate mate selection the most important thing to consider is a great point made by Pawlowski and Dunbar: finding a mate is about advertising what you have to offer while making known what you want in a mate. Then it’s all about finding some kind of compromise through a series of trade-offs based on what the individual wants, what they can offer, and what’s available in the dating pool. (So, since neither Brad Pitt nor Justin Bieber are currently in the dating pool, my previous comparison was pointless.)

Those of you who met your mate while on the pill: not to fear. I don’t think that the possibility that you may have some suppression of masculinized preferences at one point in your cycle means you’ve chosen the wrong person.

Buston PM, & Emlen ST (2003). Cognitive processes underlying human mate choice: The relationship between self-perception and mate preference in Western society. Proceedings of the National Academy of Sciences of the United States of America, 100 (15), 8805-10 PMID: 12843405

6 comments:

Although there is certainly a hormonal influence on preferences, I'm doubtful that the causal weight is strong enough for sex hormones to be singled out. For behavioral preferences, I would imagine that serum levels of sex hormones is secondary to the downstream effects that they and the chemicals that they help biosynthesize share---strengthening nerve cell integrity, neurogenesis, neuroplasticity, inflammation, excitatory potential, higher cognitive functioning, etc. Sex hormones and other related messengers share a role in influencing these processes, but they do so through distinctive mechanisms. And although sex hormones are believed to have a paternal relationship with these messengers, they should not be considered the only and most reliable biomarkers of their status. What's more critical is the varied inputs that determine the behavior of the fundamentally important hypothalamus---circadian cycles, thermoregulation, mood, and desire----which in addition to steroids, includes blood borne stimuli, environmental variables, internal stress levels, and in some cases, pathogens. So first, I would start with the hypothalamus before quantifying the role of anything else.

Returning to the role that chemical messengers have on the aforementioned processes, let me provide some examples:-Sex hormones act in part through their influence on NMDA receptors.-Dopamine has mechanistic influence through the D2 family of receptors.-Serotonin acts largely through 5ht2a receptors.The latter two of these receptors modulate Ca2 levels, which in turn, influence the NMDA receptors. The NMDA receptors release glutamate, which among other properties, importantly changes the action potential of other receptors that contribute to said processes. To be clear, though, these effects on other receptor sites aren't global---or evenly distributed, and I imagine dependent on the level of inputs. Lower levels, for instance, might lead to changes confined to dopamine and norepinephrine receptors in the dorsolateral and prefrontal cortexes---probably beta endorphin sites, and nicotinic receptors as well. Higher levels, on the other hand, might have a greater effect on dopamine and norepinephrine sites in the mesolimbic region, which would come at the expense of their relative expression in frontal cortical regions. The second outcome is strongly associated in extreme cases with behavioral disturbances in disorders ranging from Autism to some ADHD subgroups, which are distinguished in part by impaired judgement.

Returning to the behavioral effects of sex hormones, if there is a significant causal relationship between serum levels and aberrant behavior, it's likely due to their modulatory effects on the expression of NMDA and GABA receptor sites---they help to restore a balance that gives the former a moderate advantage. Moreover, for a broad spectrum of disorders, a disharmonious relationship between excitatory and inhibitory receptors seems to be an important correlate---since pharmacological agents used therapeutically for multiple conditions target this imbalance. For example, disorders defined by behavioral disturbances linked to an imbalance between these dual receptor families can be treated successfully with the same agent, even though there is a great variance in symptom severity---Huntington's, Bipolar, or Generalized Anxiety Disorder.

Therefore, because sex hormones have psychoactive effects, it's possible that the reproductive cycle---and contraceptive agents---may contribute to subtle behavioral changes of a somewhat limited significance. Lower levels of sex hormones may make nerves cells vulnerable, less communicative, and more broadly, impair general cognitive measures of functions. And generally speaking, higher levels of sex hormones should bring about an improvement in measures of general cognition, but have a detrimental effect on executive decision makings, impulse control, etc.

On a separate note, it would be useful to also test the precursors to sex hormones, since they are also psychoactive---especially pregnenolone----which would help to further illuminate the synthesis/feedback cycle. Another thing to look out for would be the relationship between sex hormones and the inflammatory cascade that 5ht2a and D2 activate. The overexpression of either can lead to schizophrenia, or progress into Autism---both disorders are strongly related. But more importantly, their combined effects on cytokine expression needs to be considered, which has an indeterminate role in symptom presentation and severity.

Putting aside chemical determinants, I think I remember reading that heaviest preferences were political orientation, physical appearance, career choice, education level, and most importantly, the mental health of the prospective partners. Also, the duration and quality of relationships don't seem to be always related to personality traits. Because two obsessive-compulsives, for instance, would be more likely to cause inter-tension. If broadly true, this means that there probably needs to have some level of difference for the sustenance of relative peace.

In any case, whatever variable that you decide on, I think you need to guard against a possible desire to overgeneralize processes that are palpably multi-variate. However, I believe your focus on hormonally determined preferences would be a good start, but at the same time, though, I think the role hormone mediated moods might have on marital stability may yield a even greater harvest.

Hmm. Anonymous, are we reading the same blog post? Because I'm pretty sure I agree with you, but you are writing as though I was making the claim that hormones do influence this behaviors significantly.

Well, that wasn't my impression, nor the purpose of my comments. However, given the mechanism of the agent in question, and because of the way that your puzzle was conveyed, I think it would be understandable if one concluded that there was an implicit suggestion that estrogen could be strongly causative.

Anyway, if my intention was interpreted as combative, I think that's owing to a lack of clarity on my part---especially my final paragraph. Indeed, rather than criticizing your entry, my comments were largely aimed at false ideas about chemical messengers that are generally subscribed to by non-professionals---like potential visitors--- that often have little appreciation for what is an unfailing multi-variate universe. With that problem in mind, I was simply trying to elucidate estrogen's place in the signaling cascade, and bring light to the uncertainty of its importance as an independent variable. But more than any other intention, this was meant to reinforce your claim, because by illustrating the role of estrogenic drugs in this sequence, I'm basically in agreement with much of the content of your post.

In any case, this blog is a small part of your public image, and because my comments are clearly vulnerable to misinterpretation, I probably should've communicated my thoughts privately. But even if that had been my choice, you shouldn't take my input that seriously---and you clearly didn't, since nearly all of my elective choices---be they undergraduate or graduate---were in the fields of political science and history. It was this distinction, the nature of your blog, and a fear of appearing ostentatious that led me post my thoughts anonymously---which in hindsight, might have the appearance of being both confrontational and cowardly.

So now that my purpose is hopefully clarified, I wish you luck with your research endeavors this Summer.

Thanks for clearing that up, Scott. No worries, it just seemed like you were trying to provide evidence in a way that was countering, rather than adding to, what I had written. I'm always glad to have commenters share their thoughts.

That's good to hear, because digital communications can sometimes present quite a barrier to communication, since it's not accompanied by body language. And although its trivial, I should probably correct my careless mistake about the mechanism of contraceptives, which of course, are anti-estrogenic, but even so, I generally dislike reducing mechanism to labels.